1. Field of the Invention
The present invention relates generally to the fields of diagnostic imaging. More particularly, it concerns methods and apparatus for generating multispectral images that may be used to diagnose various conditions in various tissues. Even more particularly, it concerns methods and apparatus for generating multispectral digital images using fluorescence, reflectance, and polarized reflectance imaging techniques.
2. Description of Related Art
Over the last fifty years, Papanicolaou Smear (xe2x80x9cPap Smearxe2x80x9d) has become the cornerstone of efforts to reduce cervical cancer mortality. Pap Smear is effective because it identifies the latest stages of cervical cancer. Current estimates are that 60-70 million Pap Smears are done in the U.S. each year. Pap Smear has thus become a norm in the detection of cervical cancer. In spite of its broad acceptance in the medical community, studies indicate that Pap Smear screenings will fail to detect from 50%-80% of low grade cancerous lesions, and even 15%-30% of high grade cancerous lesions.
When conducting Pap Smear screenings, a gynecologist collects exfoliated cells from the surface of the cervix and places them on slides that are sent to cytologists for further examination. Cytologists then review the cells placed on the slides and look for abnormal cells. If abnormal cells are found, the Pap Smear is considered to be positive. If no abnormal cells are found, the Pap Smear is considered to be negative. It is also possible that Pap Smear slides cannot be properly evaluated by the cytologist because of technical problems associated with the Pap Smear collection process such inadequate cell count, improper slide fixation, etc.
In the early stages of cervical disease, abnormal cell exfoliation is slow and most abnormal cells are located below the surface or are trapped by a keratin barrier covering the cervical surface. In these circumstances, the Pap Smear screening process is a relatively insensitive indicator of cervical health due to inaccessibility of abnormal cells that are otherwise indicators of cancerous or pre-cancerous tissue. Human Papilloma Virus (xe2x80x9cHPVxe2x80x9d) is the most common cause of keratin barriers to exfoliation. Further, it is commonly known that a significant portion of the U.S. population harbors this virus which therefore complicates the challenge of cervical cancer detection when using the Pap Smear as the principal screening procedure.
Because of a variety of problems associated with Pap Smear screening, it is well known that the Pap Smear procedure has both a high false negative, and a high false positive rate. Nevertheless, in spite of its cancer detection shortcomings, Pap Smear screening is generally recognized as a practical and economical procedure for the early detection of cervical cancer. While the Pap Smear process is designed for initial screening, colposcopy and related procedures are generally used to confirm Pap Smear abnormalities and to grade cancerous and potential cancerous lesions.
Since its introduction in 1925, colposcopy has acquired wide recognition as a follow-up clinical procedure for patients identified by Pap Smear screening as having possible cervical abnormalities. It is generally recognized that colposcopy is highly effective in evaluating patients with abnormal Pap Smears and has therefore become the standard of medical care in the Western world for this circumstance. It is estimated that approximately 4 million colposcopy examinations are currently performed in the U.S. each year. Its routine use, however, is time consuming and costly. Further, proper colposcopy examinations are limited by the expertise of the examiner.
Colposcopy is faced with its own set of challenges. It is a subjective assessment and the quality depends greatly on the expertise of the practitioner. It is time consuming with significant legal risks associated with false negative evaluations, and is therefore expensive. Certain types of computer-aided colposcopy, while capable of generating, storing and manipulating certain types of image data for the production of high-quality images, are currently unwieldy and expensive. Such colposcopes send signals to a remote computer through 5 to 7 meter long coaxial cables. As the colposcope is maneuvered to visualize the cervix, the wiring may become tangled with the patient or other equipment. Further, the remote location of the computer and video monitor prevents the patient from viewing the image as the examination is being conducted. Thus, these colposcopes provide an uncomfortable setting for the patient during examination. Further, the remote location of the video monitor also makes the viewing of the image difficult for the doctor while operating the colposcope.
Traditional colposcopes rely upon a single type of imagingxe2x80x94reflectance. However, reflectance data does not provide a complete picture of the state of tissue being examined. Further, the detector used for traditional colposcopy is most often the human eye. Therefore, accurate analysis of information obtained from the colposcope is highly dependent upon the skill of the operator in interpreting what is seen through the instrument. Although certain optical filters may be used to enhance contrast or to highlight certain types of tissue, the operator must still exhibit a relatively high level of skill to avoid false negative evaluations.
A need therefore exists in the area of cervical cancer screening and detection for apparatus and methods that may enhance or replace traditional colposcopy to allow for more accurate, real-time diagnosis. Specifically, a need exists for a technique that uses multispectral imaging techniques to provide high-resolution, two-dimensional images that may be used, for instance, to detect cervical pre-cancer.
In one respect, the invention is an apparatus for generating multispectral images of tissue. The apparatus includes an illumination source, a detector, an illumination filter, a detection filter, and an analysis unit. The illumination source is configured to illuminate the tissue with radiation. The detector is configured to collect radiation from the tissue. The illumination filter is in operative relation with the illumination source and is configured to select a first wavelength and a first polarization of radiation to be directed from the source to the tissue. As used herein, xe2x80x9cwavelengthxe2x80x9d is to be interpreted broadly to include not only a single wavelength, but a range of wavelengths as well. Similarly, as used herein, xe2x80x9cpolarizationxe2x80x9d is to be interpreted broadly to include not only a single polarization orientation, but a range of polarizations as well. The detection filter is in operative relation with the detector and is configured to select a second wavelength and a second polarization of radiation to be directed from the tissue to the detector. The analysis unit is in operative relation with the detector and is configured to generate a plurality of multispectral images of the tissue according to different combinations of first and second wavelengths and first and second polarizations.
In other respects, the first and second wavelengths may be equal. The first and second polarizations may be equal. The apparatus may also include illumination optics and imaging optics. The illumination optics may be in operative relation with the illumination source and may be configured to direct radiation from the illumination source to the tissue. The imaging optics may be in operative relation with the tissue and may be configured to direct radiation from the tissue to the detector. The illumination optics may include a fiber bundle. The detection optics may include a fiber bundle. The illumination filter may be integral with the illumination source. The detection filter may be integral with the detector. The illumination source may include a tunable pulsed laser. The illumination source may include a pulsed flashlight. The detector may include a CCD camera. The illumination filter may include a bandpass filter, a filter wheel, or a tunable filter. The tunable filter may include an acousto-optical filter or a liquid crystal filter. The detection filter may include a bandpass filter, a filter wheel, or a tunable filter. The tunable filter may include an acousto-optical filter or a liquid crystal filter. The illumination and detection filters may be integral. The tissue may include a cervix. The plurality of multispectral images may include images of approximately the entire cervix. The plurality of multispectral images may include images of fluorescence, reflectance, polarized reflectance, or any combination thereof. The apparatus may be coupled to an endoscope. The apparatus may be coupled to a colposcope. The analysis unit may also be configured to generate a composite image of the tissue, the composite image incorporating one or more features of the plurality of multispectral images. The composite image may include information relating to the size of one or more lesions of the tissue.
In another respect, the invention is a method for generating multispectral images of tissue. Primary radiation is produced with an illumination source. The primary radiation is filtered to select a first wavelength and a first polarization. The tissue is illuminated with the filtered primary radiation to generate secondary radiation. The secondary radiation is filtered to select a second wavelength and a second polarization. The filtered secondary radiation is collected with a detector. A plurality of multispectral images of the tissue are generated according to different combinations of first and second wavelengths and first and second polarization with an analysis unit in operable relation with the detector.
In other respects, the method may also include generating a composite image of the tissue, the composite image incorporating one or more features of the plurality of multispectral images. The method may also include determining the size of one or more lesions using the composite image. The plurality of multispectral images may include images of fluorescence, reflectance, polarized reflectance, or any combination thereof.